1. Field of the Invention
The present invention relates to a technology for performing the synchronization of a redundancy system. The present invention can be applied to a multimedia communication server to provide integrated data and voice communication services, for example.
2. Description of Related Art
A redundancy system has two or more devices having the same functions, and uses one of these devices for services. One device in the status of processing the service is called an “active device”, and the other one or more devices is/are called the “standby device(s)”. When the active device fails, one of the standby devices is switched to active. The failure of the device which is no longer in active status is automatically or manually recovered. The device recovered from failure becomes standby status preparing for the case when failure occurs to an active device.
The redundancy system has an advantage in that the services interruption time, when a failure occurs to a device, is short. Also the redundancy system is expected to continue services without allowing the user to recognize the occurrence of the failure.
In order to transfer to processing from the former active device to the new active device, data stored in these devices must match. If the stored data does not match, the new active device cannot succeed the services of the former active device. The processing to match the stored data of these devices is called “synchronization”. A technology to perform synchronization is disclosed in Japanese Patent Application Laid-Open No. 2001-345850. The redundancy system of this document has an information server which performs centralized management of the stored data of the CA (Call Agent), that is each device. The new active server can acquire the stored data of the former active server by reading the original data from the information server.
The redundancy system in the above document, however, cannot perform synchronization if a failure occurs to an application which provides service. Therefore if such a failure occurs, the data overwritten after the previous synchronization cannot be sent to the standby device. Because of this, the system in the above mentioned document cannot guarantee perfect synchronization.